This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Patent Application No. 11(1999)-264350 filed on Sep. 17, 1999, the entire content of which is incorporated herein by reference.
The present invention is generally related to a sensor. More particularly, the present invention pertains to a seat occupancy sensor for a vehicle seat that is usable in conjunction with various vehicle onboard systems such as an airbag actuation device and/or a seat belt warning device.
An example of a known type of seat occupancy sensor is disclosed in U.S. Pat. No. 5,896,090. This known device for detecting a seated person on a seat includes a pressure switch disposed in the seat. The pressure switch includes a pair of films and a pair of electrodes disposed between the films. The pair of electrodes are spaced in the film so as to define an OFF condition of the pressure switch. The pressure switch is in an ON condition when the electrodes contact each other. The device further includes a controller connected to the electrodes of the pressure switch to determine whether or not the seat is occupied by the person in accordance with the ON and OFF condition of the pressure switch.
With the construction of the seat occupant sensor described above, the ON condition of the pressure switch is established by deformation of the films when the seat is occupied by the person. However, if the ambient temperature is very low, the films become relatively inflexible. Under such conditions, the ON condition of the pressure switch may not be established when the seat is occupied by a person.
Thus, a need exists for a seat sensor device that is accurate and reliable under different operating conditions, including when the ambient temperature is relatively low.
According to one aspect of the present invention, a seat occupancy sensor includes an optical wave guide provided in the seat for allowing the passage of light. The optical wave guide has a light transmissive portion possessing a curvature that is variable, with the optical wave guide changing the physical quantity of the light passing through the light transmissive portion when the curvature varies as a result of occupancy of the seat. The sensor also includes a light emitting device for inputting light into the optical wave guide, a light receiving device for receiving light outputted from the optical wave guide, and a detecting device which detects occupancy of the seat when the physical quantity of light passing through the light transmissive portion changes due to a change in the curvature of the transmissive portion as a result of the occupancy of the seat.
The occupancy of the seat, by a person or an object other than a person such as baggage, applies a load on the optical wave guide to cause the change in the curvature of the light transmissive portion of the optical wave guide. Thus, the physical quantity of the light passing through the optical wave guide also changes. Typically, the physical quantity is the amount of light. In the case where the light is a laser beam, its phase of wavelength can be used as the physical quantity.
As the physical quantity of the transmissive light changes, the light received at the light receiving means changes accordingly. On the basis of this, the detecting device determines whether or not the seat is occupied. The seat can be a vehicle seat as well as other types of seats such as a chair, a toilet seat, etc. In the case of vehicle seats, the present invention has application to the driver""s seat, the front passenger seat and the rear seat.
In accordance with the present invention, an optical fiber can be used as the optical wave guide. The optical fiber can be formed of plastic or quartz, with the plastic optical fiber being highly useful from the standpoint of being well suited to avoiding potential damage.
Depending upon the circumstances, the optical wave guide can also be formed by providing a thin film having optical guide properties onto a substrate so as to be in a layer structure. To permit a change in the curvature upon occupancy of the seat, the substrate is preferably flexible.
The light emitting means can be in the form of a light emission element which converts electric signals to light such as a light emission diode (LED) or a laser element which emits a coherent, high-directive laser beams is possible. Devices emitting either visible or invisible light can be employed, and either laser beam or non-laser beam is acceptable. In the case of visible light, color is not limited and therefore red light, blue light, green light, yellow light, deep blue light and so on, can be employed.
The light receiving means can be in the form of a light receiving element which converts received light into electric signal such as a photo-transistor, photo-diode or the like.
The transmissive portion of the optical wave guide possesses a bent portion that is adapted to have its curvature changed to thereby change the physical quantity of the light passing through the optical wave guide when upon occupancy of the seat. The bent portion can take anyone of a variety of different forms including a loop, a U-shaped structure, an inverted U-shaped structure, a V-shaped structure, and an inverted V-shaped structure. It is also possible to form the transmissive portion as a plurality of bent portions. For example, the bent portion can be formed as a coil-like structure having plural loops, or can be formed as a repeating alternating series of the other mentioned structures.
The detecting device can be structured to detect occupancy of the seat depending on the difference between the emitted light signal of the light emitting means and the light receiving signal received by the light receiving means. The detecting device can also have the distinct function of distinguishing whether the seat is occupied by a person or a non-person object such as baggage. In general, the weight of a person, especially an adult, is greater than that of an object such as baggage. Using this empirical knowledge, it is possible to distinguish between a person and baggage occupying the seat based on the curvature change of the bent portion which varies with the applied load.
The detecting device can also be designed to perform a distinguishing function based on a difference between the emitted light signal of the light emitting means and the light receiving signal received by the light receiving means. As the difference, either the amount of time delay of the received light relative to the emitted light or the magnitude of the changing rate of such a time delay can be utilized. If an object other than a human body is seated on the seat, the frequency of the behavior or movement of the object is quite small or non-existent. In contrast, when a person (i.e., a human body) sits on the seat, the frequency of the individual""s movements is very high. It is thus possible to relatively easily recognize whether a person is seated on the seat or whether instead some other object is seated on the seat by measuring the frequency of change of the physical quantity of light passing through the transmissive portion of the optical wave guide. For example, be monitoring or measuring the magnitude of the changing rate of the time delay, it is possible to readily easily determine whether a person or baggage is on the seat.
A voltage signal having a rising leading edge and a falling trailing edge can be inputted to the light emitting means in pulses. Because the initial stage of light emission at the light emitting means involves a relatively small amount of emitted light, this can be used to make clear the difference between the emitted signal and the received signal such as the time difference or voltage difference. The rising leading edge can be obtained by employing a wave shape voltage such as serration-shaped wave. Also, waves such as a triangle wave, sine wave, trapezoid wave and the like can be employed. If necessary, a rectangular wave and others can also be used.
According to another aspect of the present invention, an occupancy detectable seat includes a seat portion with respect to which a person is to be seated, a light emitter adapted to emit light, an optical wave guide provided in the seat portion and including an input portion connected to the light emitter to receive light emitted by the light emitter and an output portion which is connected to a light receiver that receives light outputted from the optical wave guide. The optical wave guide is adapted to change a physical quantity of light passing through the optical wave guide upon application of a load to the optical wave guide associated with occupancy of the seat portion. In addition, a detecting device detects occupancy of the seat portion based on the change in the physical quantity of light passing through the optical wave guide due to application of the load to the optical wave guide associated with occupancy of the seat portion.
According to a further aspect of the invention, a seat occupancy sensor for determining occupancy of a seat includes a light emitter, an optical wave guide, a light receiver and a detecting device. The light emitter is connected to an input portion of the optical wave guide for emitting light and the light receiver is connected to an output portion of the optical wave guide for receiving light outputted from the optical wave guide. The optical wave guide is adapted to be positioned in the seat and to change a physical quantity of light passing through the optical wave guide upon application of a load to the optical wave guide associated with occupancy of the seat. The detecting device detects occupancy of the seat based on the change in the physical quantity of light passing through the optical wave guide due to application of the load to the optical wave guide associated with occupancy of the seat.